What does 1 Kings 20:23 mean?

Meanwhile, the officials of the king of Aram said to him, 'Their god is a god of the hills. That’s why they beat us. If we fight them on the plains, we’ll win.' 1 Kings 20:23 - Modern Text Bible

(Ben-Hadad’s advisors think Israel’s God only has power in the hills, so they plan to fight on flat ground next time.)